Altronics FM Microphone

This Altronics FM Microphone kit I did get to work unlike the Jaycar kit. The main difference is the inductor which is preformed as a PCB track in the Altronics kit. Transmission is extremely temperamental though I may have made a bad solder joint somewhere. When it does transmit on a stable frequency though, the sound is crystal clear (or at least it is sat in my car, using the radio.)

The condenser microphone and R1 form a variable voltage divider, C1 allows only the AC to pass, R2 and R3 form a static voltage divider and C2, C3 eliminate ripple to the base of transistor Q1. The two voltage dividers change the amount of feedback going to the LC tank L1, CV1 and therefore the frequency at which the LC tank oscillates. Inductor L1 is responsible for creating the electromagnetic field- radio waves!